TECHNICAL FIELD
[0001] The present disclosure relates to a film capacitor, a connected capacitor, an inverter
including the connected capacitor, and an electric vehicle.
BACKGROUND OF INVENTION
[0002] A known technique is described in, for example, Patent Literature 1.
CITATION LIST
PATENT LITERATURE
SUMMARY
[0004] In an aspect of the present disclosure, a film capacitor includes a stack including
at least one dielectric film including a polyarylate film and a plurality of metal
vapor deposition films being alternate to each other, cover films containing a polyester
hot-melt resin and located on two first side surfaces of the stack opposite to each
other in a first direction orthogonal to a stacking direction of the stack, and metal-sprayed
electrodes on two second side surfaces of the stack opposite to each other in a second
direction perpendicular to the first direction and orthogonal to the stacking direction.
[0005] In another aspect of the present disclosure, a connected capacitor includes a plurality
of film capacitors including the above film capacitor, and a busbar connecting the
plurality of film capacitors.
[0006] In another aspect of the present disclosure, an inverter includes a bridge circuit
including a switching element, and a capacitance portion connected to the bridge circuit.
The capacitance portion includes the above film capacitor.
[0007] In another aspect of the present disclosure, an electric vehicle includes a power
supply, an inverter connected to the power supply and being the above inverter, a
motor connected to the inverter, and wheels drivable by the motor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The objects, features, and advantages of the present disclosure will become more
apparent from the detailed description and the drawings described below.
FIG. 1 is a perspective view of an example stacked film capacitor according to an
embodiment of the present disclosure.
FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1.
FIG. 3 is a cross-sectional view taken along line III-III in FIG. 1.
FIG. 4 is a schematic diagram of a test piece for examining the bonding state.
FIG. 5 is a perspective view of an example connected capacitor.
FIG. 6 is a schematic diagram describing an example inverter.
FIG. 7 is a schematic diagram of an example electric vehicle.
DESCRIPTION OF EMBODIMENTS
[0009] A stacked film capacitor that forms the basis of a stacked film capacitor according
to one or more embodiments of the present disclosure typically includes a body cut
from an elongated stack and thus is to have cut surfaces with improved insulation.
Patent Literature 1 describes a stacked polypropylene film capacitor including polypropylene
films as dielectric films and including cover films containing a polyolefin hot-melt
resin melted and bonded externally to exposed two side surfaces that are adjacent
to two side surfaces with metal-sprayed electrodes. The cover films reduce discharge
from the two externally exposed side surfaces under a voltage being applied.
[0010] FIG. 1 is a perspective view of an example stacked film capacitor according to an
embodiment of the present disclosure. FIG. 2 is a cross-sectional view taken along
line II-II in FIG. 1. FIG. 3 is a cross-sectional view taken along line III-III in
FIG. 1. As illustrated in FIGs. 1 to 3, a stacked film capacitor A includes a film
capacitor body 3 and a pair of a first metal-sprayed electrode 4a and a second metal-sprayed
electrode 4b. The film capacitor body 3 may also be simply referred to as the body
3. The body 3 includes a stack of first dielectric films 1a, first metal vapor deposition
films 2a, second dielectric films 1b, and second metal vapor deposition films 2b.
The body 3 is rectangular and includes a pair of first surfaces 3a and 3b opposite
to each other in the stacking direction in which the dielectric films and the metal
vapor deposition films are stacked, a pair of first side surfaces 3c and 3d, and a
pair of second side surfaces 3e and 3f. The pairs are both located between the first
surfaces 3a and 3b to connect the first surfaces 3a and 3b. In the figures referred
to below, the dimensions of the components of the body 3 are exaggerated for ease
of explanation. The thicknesses of the actual components are much smaller than the
thicknesses of the illustrated components of the body 3.
[0011] The first metal-sprayed electrode 4a is formed on the first side surface 3c of the
body 3, and the second metal-sprayed electrode 4b is formed on the first side surface
3d of the body 3 both through metal spraying. Cover films 16a and 16b that are electrically
insulating are located on the second side surfaces 3e and 3f of the body 3.
[0012] As illustrated in FIG. 2, the body 3 in the stacked film capacitor A includes first
metalized films 6a and second metalized films 6b that are alternately stacked on each
other. Each first metalized film 6a includes the first metal vapor deposition film
2a on a surface 1ac of the first dielectric film 1a. Each second metalized film 6b
includes the second metal vapor deposition film 2b on a surface 1bc of the second
dielectric film 1b. Each first metal vapor deposition film 2a is electrically connected
to the first metal-sprayed electrode 4a on the first side surface 3c of the body 3.
Each second metal vapor deposition film 2b is electrically connected to the second
metal-sprayed electrode 4b on the first side surface 3d of the body 3. As illustrated
in FIG. 1, a first direction x refers to the direction in which the first metal-sprayed
electrode 4a and the second metal-sprayed electrode 4b are located, and a second direction
y refers to the direction in which the cover films 16a and 16b are located. A third
direction z refers to the thickness direction of the first dielectric films 1a and
the second dielectric films 1b, or more specifically, the stacking direction.
[0013] Each first metalized film 6a includes the first dielectric film 1a and the first
metal vapor deposition film 2a on the surface 1ac. Each first metalized film 6a includes,
on the surface 1ac adjacent to a side surface 1af without the first metal vapor deposition
film 2a being formed, or in other words, in an area on which the first dielectric
film 1a is exposed, an insulating margin 7a extending continuously in the second direction
y.
[0014] Each second metalized film 6b includes the second metal vapor deposition film 2b
on the surface 1bc of the second dielectric film 1b. Each second metalized film 6b
includes, on the surface 1bc adjacent to a side surface 1bf without the second metal
vapor deposition film 2b being formed, or in other words, in an area on which the
second dielectric film 1b is exposed, an insulating margin 7b extending continuously
in the second direction y.
[0015] As illustrated in FIG. 2, the metalized films 6a and 6b are stacked on each other
with a slight deviation from each other in the first direction x, which is also referred
to as the width direction.
[0016] Any potential difference between the first metal vapor deposition film 2a and the
second metal vapor deposition film 2b generates capacitance in an active area 8 in
the first metal vapor deposition film 2a and the second metal vapor deposition film
2b overlapping each other across the first dielectric film 1a or the second dielectric
film 1b.
[0017] The stacked film capacitor A described above is obtained in the manner described
below. The first metalized film 6a and the second metalized film 6b that are both
elongated are stacked on each other with a slight deviation from each other in the
first direction x or the width direction, thus forming a stack. The first metal-sprayed
electrode 4a is formed on the first side surface 3c in the first direction x of the
resultant stack, and the second metal-sprayed electrode 4b is formed on the first
side surface 3d. The stack including the metal-sprayed electrodes 4, or specifically
the first metal-sprayed electrode 4a and the second metal-sprayed electrode 4b, is
cut in the first direction x into individual elements. The metal-sprayed electrodes
4 may be formed on the individual bodies 3 cut from the stack. The cut surfaces resulting
from the stack being cut are the second side surfaces 3e and 3f of the bodies 3.
[0018] The features common to the first metalized film 6a and the second metalized film
6b in the stacked film capacitor A according to the present embodiment will be described
below. In FIG. 3, the components may be simply referred to as dielectric films 1,
metal vapor deposition films 2, the metal-sprayed electrodes 4, or metalized films
6 without the reference signs a and b.
[0019] As illustrated in FIGs. 1 to 3, in the present embodiment, the film capacitor A includes,
among the four side surfaces 3c, 3d, 3e, and 3f of a film capacitor device 12 including
the stack of the metalized film 6a and 6b, the two side surfaces 3e and 3f adjacent
to the other two side surfaces 3c and 3d with the metal-sprayed electrodes 4a and
4b. The side surfaces 3e and 3f are located on the two ends of the film capacitor
device 12 in the length direction (lateral direction in FIG. 3) and are entirely covered
with cover films 16a and 16b for separation from outside. The two cover films 16a
and 16b are melted and bonded (bonded by melting) to the side surfaces of the dielectric
films 1a and 1b in the metalized films 6a and 6b exposed on the side surfaces 3e and
3f.
[0020] In the present embodiment, the film capacitor A is thus less likely to have a leakage
current from the two side surfaces 3e and 3f, and can have a longer creepage distance
between the metal vapor deposition films 2a and 2b in the metalized films 6a and 6b
to reduce short-circuiting resulting from discharge between the metal vapor deposition
films 2a and 2b and to have an improved withstand voltage. The side surfaces of the
dielectric films 1a and 1b in the metalized films 6a and 6b exposed on the side surfaces
3e and 3f are fully in close contact with the cover films 16a and 16b to prevent entry
of moisture and air between the side surfaces of the dielectric films 1a and 1b (and
thus the side surfaces of the metalized films 6a and 6b) and the cover films 16a and
16b.
[0021] The two cover films 16a and 16b include polyester hot-melt films containing a polyester
hot-melt resin similar to polyarylate in the dielectric films 1a and 1b in the metalized
films 6a and 6b and having high performance in thermal melting and bonding (melting
and bonding performance) to polyarylate. Using the two cover films 16a and 16b containing
the resin material, the cover films 16a and 16b are melted and bonded reliably and
firmly to the side surfaces of the dielectric films 1a and 1b in the metalized films
6a and 6b exposed on the two side surfaces 3e and 3f of the film capacitor device
12.
[0022] FIG. 4 is a schematic diagram of a test piece for examining the bonding state. A
polyethylene terephthalate plate B containing a resin similar to polyarylate was bonded
to a rectangular plate A with a vertical width a of 25 mm, a horizontal width b of
33 mm, and a thickness t of 2 to 5 mm including a polyarylate plate by heat treatment
at 100 °C. A polycarbonate plate B was also bonded to a rectangular plate A by heat
treatment at 180 °C. The bonding state of each test piece was examined to reveal that
the polyethylene terephthalate plate and the polycarbonate plate were both bonded
firmly to the polyarylate plates.
[0023] The two cover films 16a and 16b are to contain a polyester hot-melt resin, although
the two cover films 16a and 16b may contain a polyester hot-melt resin of any type
or with any structure. More specifically, various known polyester hot-melt resins
can be used as a material for the two cover films 16a and 16b.
[0024] The two cover films 16a and 16b including such a polyester hot-melt resin are formed
to cover the entire surfaces of the side surfaces 3e and 3f of the film capacitor
device 12 using, for example, the methods described below.
[0025] The first method is, for example, to form a film of polyester hot-melt resin with
a predetermined thickness by spraying the polyester hot-melt resin in a melted state
with heat onto the entire side surfaces 3e and 3f of the film capacitor device 12
using a nozzle or by applying the resin using a roller. The ends of the metalized
films 6a and 6b including the side surfaces of the dielectric films 1a and 1b exposed
on the side surfaces 3e and 3f of the film capacitor device 12 are then melted with
the heat of the polyester hot-melt resin in a melted state. These components are then
cooled to solidify. This allows the two cover films 16a and 16b each containing the
polyester hot-melt film to cover the entire side surfaces 3e and 3f of the film capacitor
device 12 and to be melted and bonded to the side surfaces of the dielectric films
1a and 1b.
[0026] The second method is, for example, to form a polyester hot-melt film on the entire
side surfaces 3e and 3f of the film capacitor device 12, and heat and melt the polyester
hot-melt film. The ends including the side surfaces of the dielectric films 1a and
1b in the metalized films 6a and 6b exposed on the side surfaces 3e and 3f of the
film capacitor device 12 may be melted. These components are then cooled to solidify.
This also allows the two cover films 16a and 16b to cover the entire side surfaces
3e and 3f of the film capacitor device 12 and to be melted and bonded to the side
surfaces of the dielectric films 1a and 1b. The polyester hot-melt film to be formed
on the side surfaces 3e and 3f of the film capacitor device 12 may be, for example,
an extruded product in a semi-melted state formed with a predetermined die, in addition
to a common film.
[0027] The cover films 16a and 16b on the side surfaces 3e and 3f of the film capacitor
device 12 may have any thickness that may be, for example, about 0.1 to 1000 µm. The
cover films 16a and 16b with a thickness of less than 0.1 µm may be too thin to achieve
a sufficiently long creepage distance of the metal vapor deposition films 2a and 2b
in the metalized films 6a and 6b and to have a sufficiently improved withstand voltage.
The cover films 16a and 16b having a thickness exceeding 1000 µm may not achieve an
improved effect and may have, for example, an increased cost of the cover films 16a
and 16b. The cover films 16a and 16b may thus have a thickness of less than or equal
to 1000 µm.
[0028] The polyester hot-melt resin in the two cover films 16a and 16b may have a lower
melting point than polyarylate in the dielectric films 1a and 1b and have high wettability
with the polyarylate to heat and melt the side surfaces of the dielectric films 1a
and 1b in the metalized films 6a and 6b to which the cover films 16a and 16b are melted
and bonded. A material with high wettability maintains the bonding strength with the
polyarylate.
[0029] In manufacturing the film capacitor device 12, elongated protective films are formed
on the two end faces of an elongated stack including multiple elongated metalized
films 6a and 6b that are stacked alternately with a deviation between them in the
width direction to form an elongated film capacitor device base material. This base
material is then cut in the width direction using a cutting blade such as a rotary
saw blade at, for example, multiple positions at a predetermined distance between
them in the length direction. This produces multiple film capacitor devices 12 at
a time. The two side surfaces 3c and 3d of the film capacitor device 12 in the width
direction are the surfaces to receive the two metal-sprayed electrodes 4a and 4b,
whereas the two side surfaces 3e and 3f of the film capacitor device 12 in the length
direction, including the cut surfaces of the film capacitor base material, are the
surfaces to receive the two cover films 16a and 16b.
[0030] When the cover films 16a and 16b are applied at temperatures greatly exceeding 220
°C, which is the glass transition point (Tg) of polyarylate, the film capacitor device
12 can soften and deform or cause self-healing failure. Thus, the cover films 16a
and 16b contain a polyester resin with a melting point of 150 to 250 °C that is less
than or similar to the glass transition point Tg of 220 °C with high wettability and
with a glass transition point Tg of 50 to 160 °C.
[0031] The polyester hot-melt resin in the cover films 16a and 16b has a lower melting point
than polyarylate as a resin material in the dielectric films 1a and 1b. The polyester
hot-melt resin as the material in the cover films 16a and 16b thus reduces deformation
of the dielectric films 1a and 1b, and reduces self-healing failure resulting from
the heat of the polyester hot-melt resin in a melted state in the cover films 16a
and 16b when the cover films 16a and 16b are melted and bonded to the side surfaces
3e and 3f of the dielectric films 1a and 1b (when the cover films 16a and 16b are
formed on the side surfaces 3e and 3f of the film capacitor device 12). The polyester
hot-melt resin with a low glass transition point Tg has high wettability with polyarylate
and maintains the bonding strength with polyarylate, thus reducing the likelihood
that the cover films 16a and 16b melted and bonded to the dielectric films 1a and
1b are separate from the dielectric films 1a and 1b. This structure can satisfy the
operating temperatures of 125 to 150 °C for high-temperature resistant film capacitors.
[0032] The polyester hot-melt resin in the cover films 16a and 16b has a melt viscosity
in the range of 500 to 50000 mPa·s at 150 to 250 °C.
[0033] As described above, in the present embodiment, the film capacitor A includes the
two cover films 16a and 16b covering the entire surfaces of the remaining two side
surfaces 3e and 3f other than the side surfaces 3c and 3d to receive the metal-sprayed
electrodes 4a and 4b to reduce a leakage current from the two side surfaces 3e and
3f and provide a longer creepage distance between the metal vapor deposition films
2a and 2b of the metalized films 6a and 6b. The two cover films 16a and 16b containing
the polyester hot-melt resin are melted and bonded to the side surfaces of the dielectric
films 1a and 1b including polyester of the metalized films 6a and 6b exposed on the
two side surfaces 3e and 3f. The side surfaces of the dielectric films 1a and 1b are
thus fully in close contact with the cover films 16a and 16b without small gaps between
them. This effectively and reliably reduces the entry of water vapor or air between
the side surfaces of the dielectric films 1a and 1b and the cover films 16a and 16b.
This is combined with an increase in the creepage distance between the metal vapor
deposition films 2a and 2b to reduce degradation of the dielectric films 1a and 1b
and the metal vapor deposition films 2a and 2b due to contact with water vapor. This
also reduces discharge between the metal vapor deposition films 2a and 2b to effectively
improve the withstand voltage.
[0034] The surfaces of the metal vapor deposition films 2a and 2b and the metal-sprayed
electrodes 4a and 4b are oxidized to contain Al-O-Al, a hydroxyl group, or a carboxyl
group. A polyolefin resin used for known cover films is a low polar resin and contains
no carboxyl group or no hydroxyl group. The polyolefin resin thus interacts less with
a metal oxide (with low van der Waals force and without a hydrogen bond). A polyester
resin used for the cover films 16a and 16b is a polar resin, and contains an ether
bond, a carbonyl group, a carboxyl group, or a hydroxyl group, which interacts highly
with a metal oxide (with high van der Waals force and including a hydrogen bond).
The cover films 16a and 16b in the present embodiment interact with the metal vapor
deposition films 2a and 2b and with the metal-sprayed electrodes 4a and 4b more than
known cover films. This effectively reduces the likelihood that the cover films 16a
and 16b melted and bonded to the side surfaces 3e and 3f are separated.
[0035] The film capacitor A simply including the thin cover films 16a and 16b, each including
a resin film, on the two side surfaces 3e and 3f may produce the advantageous features
described above. The above features can be achieved without the entire film capacitor
A becoming larger or the costs becoming higher.
[0036] Thus, the film capacitor according to the present embodiment can substantially reduce
a leakage current, maintain the expected capacitor performance stably for a longer
period, and improve the withstand voltage without increasing the size or the production
cost of the film capacitor.
[0037] FIG. 5 is a schematic perspective view of a connected capacitor in an example. In
FIG. 5, a case and an external resin covering the capacitor surface are not illustrated
for ease of explanation. A connected capacitor C includes multiple stacked film capacitors
connected in parallel with a pair of busbars 21 and 23. The busbars 21 and 23 include
terminals 21a and 23a for external connection and lead terminals 21b and 23b. The
lead terminals 21b and 23b are connected to the corresponding metal-sprayed electrodes
4a and 4b in the film capacitor.
[0038] The film capacitor in the connected capacitor C may include the film capacitor A
with the cover films 16a and 16b. The resultant connected capacitor C may have insulation
resistance less likely to decrease.
[0039] The connected capacitor C may include at least one film capacitor A, and may include
two or more film capacitors A. The connected capacitor C includes multiple film capacitors,
for example, four capacitors aligned with one another as illustrated in FIG. 4, and
includes the busbars 21 and 23 attached to the metal-sprayed electrodes at the two
ends of the body 3 with a bond.
[0040] The connected capacitor C may include the film capacitors arranged horizontally as
illustrated in FIG. 5 or stacked vertically. The film capacitors may be arranged in
the direction perpendicular to the first direction x in which the metal-sprayed electrodes
4 are located.
[0041] FIG. 6 is a schematic diagram describing an example inverter. FIG. 6 illustrates
an inverter D that converts direct current (DC) to alternating current (AC). As illustrated
in FIG. 6, the inverter D includes a bridge circuit 31 and a capacitance portion 33.
The bridge circuit 31 includes switching elements such as insulated-gate bipolar transistors
(IGBTs) and diodes. The capacitance portion 33 is across the input terminals of the
bridge circuit 31 to stabilize the voltage. The inverter D includes the film capacitor
A as the capacitance portion 33.
[0042] The inverter D is connected to a booster circuit 35 that raises the voltage of a
DC power supply. The bridge circuit 31 is connected to a motor generator M as a drive
source.
[0043] FIG. 7 is a schematic diagram of an electric vehicle. FIG. 7 illustrates a hybrid
electric vehicle (HEV) as an example of the electric vehicle.
[0044] The electric vehicle E includes a motor 41, an engine 43, a transmission 45, an inverter
47, a power supply (battery) 49, front wheels 51a, and rear wheels 51b.
[0045] The electric vehicle E includes an output unit, such as the motor 41, the engine
43, or both, as the drive source. The output from the drive source is transmitted
to the pair of left and right front wheels 51a through the transmission 45. The power
supply 49 is connected to the inverter 47, which is connected to the motor 41.
[0046] The electric vehicle E illustrated in FIG. 7 also includes a vehicle electronic control
unit (ECU) 53 and an engine ECU 57. The vehicle ECU 53 centrally controls the entire
electric vehicle E. The engine ECU 57 controls the rotational speed of the engine
43 and drives the electric vehicle E. The electric vehicle E further includes an ignition
key 55 operable by, for example, a driver, and driving components such as an accelerator
pedal and a brake (not illustrated). The vehicle ECU 53 receives an input drive signal
in response to an operation on a driving component performed by, for example, the
driver. The vehicle ECU 53 outputs, based on the drive signal, an instruction signal
to the engine ECU 57, the power supply 49, and the inverter 47 as a load. In response
to the instruction signal, the engine ECU 57 controls the rotational speed of the
engine 43 and drives the electric vehicle E.
[0047] The inverter 47 in the electric vehicle E includes the inverter D, which includes
the film capacitor A as the capacitance portion 33. The electric vehicle E includes
the film capacitor A that has insulation resistance less likely to decrease. In a
harsh environment such as in an engine part of the electric vehicle E, the film capacitor
A may have insulation resistance less likely to decrease over a long period. The electric
vehicle E thus allows more stable current control performed by controllers such as
ECUs.
[0048] In addition to HEVs, the inverter D in the embodiment is also applicable to various
power converting products such as electric vehicles (EVs), fuel cell vehicles, electric
bicycles, power generators, and solar cells.
[0049] The present disclosure may be implemented in the following forms.
[0050] In one or more embodiments of the present disclosure, a film capacitor includes a
stack including at least one dielectric film including a polyarylate film and a plurality
of metal vapor deposition films being alternate to each other, cover films containing
a polyester hot-melt resin and located on two first side surfaces of the stack opposite
to each other in a first direction orthogonal to a stacking direction of the stack,
and metal-sprayed electrodes on two second side surfaces of the stack opposite to
each other in a second direction perpendicular to the first direction and orthogonal
to the stacking direction.
[0051] In one or more embodiments of the present disclosure, a connected capacitor includes
a plurality of film capacitors including the above film capacitor, and a busbar connecting
the plurality of film capacitors.
[0052] In one or more embodiments of the present disclosure, an inverter includes a bridge
circuit including a switching element, and a capacitance portion connected to the
bridge circuit. The capacitance portion includes the above film capacitor.
[0053] In one or more embodiments of the present disclosure, an electric vehicle includes
a power supply, an inverter connected to the power supply and being the above inverter,
a motor connected to the inverter, and wheels drivable by the motor.
[0054] In one or more embodiments of the present disclosure, the film capacitor can reduce
discharge from the metal vapor deposition films due to gaps between the cover films
and the metal vapor deposition films.
[0055] In one or more embodiments of the present disclosure, the connected capacitor can
have insulation resistance less likely to decrease.
[0056] In one or more embodiments of the present disclosure, the inverter includes the film
capacitor that can have insulation resistance less likely to decrease.
[0057] In one or more embodiments of the present disclosure, the electric vehicle allows
more stable current control performed by the controllers such as the ECUs.
[0058] Although the embodiments of the present disclosure have been described in detail,
the present disclosure is not limited to the embodiments described above, and may
be changed or varied in various manners without departing from the spirit and scope
of the present disclosure. The components described in the above embodiments may be
entirely or partially combined as appropriate unless any contradiction arises.
REFERENCE SIGNS
[0059]
- A
- film capacitor
- C
- connected capacitor
- D
- inverter
- E
- electric vehicle
- 1, 1a, 1b
- dielectric film
- 2, 2a, 2b
- metal vapor deposition film
- 3
- body
- 3a, 3b
- first surface
- 3c, 3d
- first side surface
- 3e, 3f
- second side surface
- 4, 4a, 4b
- metal-sprayed electrode
- 6, 6a, 6b
- metalized film
- 7, 7a, 7
- binsulating margin
- 12
- film capacitor device
- 16a, 16b
- cover film
- 21, 23
- busbar
- 31
- bridge circuit
- 33
- capacitance portion
- 35
- booster circuit
- 41
- motor
- 43
- engine
- 45
- transmission
- 47
- inverter
- 49
- power supply
- 51a
- front wheel
- 51b
- rear wheel
- 53
- vehicle electronic control unit (ECU)
- 55
- ignition key
- 57
- engine electronic control unit (ECU)